1. Field of the Invention
The present invention relates to a light-emitting semiconductor device using gallium nitride group compound which emits a light in the region from blue to ultraviolet, and also to a process for producing the same.
2. Description of the Prior Art
It is known that GaN compound semiconductor can be made into a light-emitting semiconductor device, such as a light-emitting diode (LED), which emits a blue light.
The GaN compound semiconductor attracts attention because of its high light-emitting efficiency resulting from a direct transition and of its ability to emit a blue light which is one of the three primary colors.
The light-emitting diode of GaN compound semiconductor is composed of a sapphire substrate, an n-layer and an i-layer grown thereon. The n-layer of the GaN compound semiconductor with n-type conduction is directly grown on the surface of the sapphire substrate or grown on a buffer layer of aluminum nitride formed on the sapphire substrate. The i-layer of semi-insulating (i-type) GaN compound semiconductor is doped with p-type impurities. (See Japanese Patent Laid-open Nos. 119196/1987 and 188977/1988.)
The voltage for driving this light-emitting diode, however, is high. Consequently, there is room for improvement.
Another disadvantage of the gallium nitride compound semiconductor is that it does not become p-type but remains i-type (semi-insulator) even though it is doped with p-type impurities.
As the results of extensive studies, the present inventors succeeded in producing a p-type gallium nitride compound semiconductor. This led to the creation of a pn junction that emits a blue light efficiently.
The light-emitting diode comprising the pn junction, however, presents a problem associated with insulating the electrode for a lower layer from an upper layer in case that the electrode for the lower layer is formed through the upper layer to get the electrode on the upper layer, because the p-layer and n-layer are electrically conductive.